From Chokutō to Tachi — The Warabite-tō and the Birth of the Japanese Sword's Form

The Kofun-Period Sword Was “Not Curved”

The beautifully curved blade that we associate today with the “Japanese sword” is, in fact, a relatively late arrival in the history of blades on the Japanese archipelago. In the Kofun period (4th-7th c.), the swords circulating on these islands were mostly chokutō — straight, double- or single-edged blades.

A representative example is the Shōsōin treasure Kingin-den-kazari no Karadachi, richly decorated in gold and silver. Its lineage of craftsmanship, along with the design of its guard and mounts, is strongly continental, reflecting Chinese and Korean influence. Blades of this period sit in too different a context to be called “Japanese swords” in the later sense.

The Warabite-tō — Sword of the Emishi in the Northeast

From the Nara into the early Heian period, a distinctive blade emerged in the region of the Emishi in northeastern Japan: the warabite-tō. The name derives from the pommel, which curls like the young shoot of a bracken fern.

Key features of the warabite-tō:

• Short grip, with a slight curve
• Easy to wield one-handed from horseback
• Suited to the mounted combat at which the Emishi excelled

This was a local innovation distinct from the continental chokutō, and it would eventually be absorbed into the central military culture. In the late 9th century, Emperor Kanmu’s campaigns against the Emishi brought the smithing techniques and mounted combat style of the northeast into the mainstream martial vocabulary.

Why Did a Curve Become Necessary?

In the mid-Heian (10th-11th c.), the curved tachi that leads directly to the modern Japanese sword takes shape. There is no single reason for the appearance of the curve, but three factors converged.

1. Adaptation to mounted combat

When cutting downward from horseback with one hand, a curved blade makes the tip naturally strike the target — a straight blade would not align to the correct angle. The lesson of the warabite-tō was absorbed at the center.

2. A byproduct of quenching (yaki-ba)

The Japanese sword’s distinctive quenching — rapid cooling of the edge alone, with the spine cooled slowly — produces a differential expansion between edge and spine that causes the blade to curve naturally. Rather than being a shape aimed at directly, the curve became a feature that could be usefully exploited as smiths refined their yaki-ba technique.

3. Efficiency of the “cutting” motion

A curved blade cuts more deeply in a drawing motion. Against the “chop” of a straight blade, the “draw-cut” of a curved tachi was more effective in real combat aimed at the gaps in armor.

The Mid-Heian Period — Completion of the “Tachi”

One of the Tenka Goken, Mikazuki Munechika (late Heian, ca. 11th century, and among the oldest surviving Japanese swords), preserves for us the tachi form as it took shape at this time. Attributed to Sanjō Munechika (Yamashiro province), it is characterized by an elegant koshi-zori posture — the deepest curve near the hilt end, rather than at the middle.

The basic form established here:

• Cutting edge around 70-80 cm
• Koshi-zori (curve deepest near the hilt)
• Shinogi-zukuri / iori-mune — a distinctive pentagonal cross-section
• Hamon — the boundary line of the quenched edge, in shapes such as suguha (straight) and midareba (irregular)

This became the basic format of the Japanese sword that would not be shaken through the Kamakura, Nanbokuchō, or Sengoku periods.

Tachi vs. Uchigatana

A key distinction to keep in mind is between the tachi and the uchigatana (later called katana):

• Tachi — Mainstream from the Heian through the Nanbokuchō. Worn with the cutting edge down, suspended from the belt. The signature (mei) is cut on the outward-facing side when worn.
• Uchigatana — Mainstream from mid-Muromachi onward. Worn with the cutting edge up, thrust through the belt. The signature is cut on the outward-facing side when thrust.

All the mid-Heian Japanese swords discussed in this article are tachi. The age of the uchigatana — foot combat, quick-drawing culture — is still 400 years in the future.

From This Article to the Next

The form of the curved Japanese sword is now complete. But the schools that would define who makes it and how are not yet in place. The next article turns to the Gokaden (Yamato, Yamashiro, Bizen, Sōshū, Mino) — the five great producing regions of Japan — as they emerge from the late Heian into the Kamakura period.